Variable speed drive for internal combustion engine

ABSTRACT

A variable speed drive wherein an impact to be transmitted to an inputting mechanism is absorbed. A shift spindle has an input side end portion to which an inputting mechanism is connected and an output side end portion supported for rotation at a transmission side supporting portion provided on a transmission case. A master arm is positioned between the input side end portion and the output side end portion in an axial direction of the shift spindle. An extension collar member is fixed integrally to the master arm. The extension collar member connects the master arm and a connection portion provided at a location of the shift spindle rather near to the input side end portion than the output side end portion. The extension collar member extends from the connection portion toward the master arm with a gap left from an outer circumferential face of the shift spindle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to JapanesePatent Application No. 2014-071772 filed Mar. 31, 2014 the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable speed drive for driving atransmission mechanism of an internal combustion engine.

2. Description of Background Art

Conventionally, a variable speed drive for driving a transmissionmechanism of an internal combustion engine includes a shift motor forrotating a shift spindle for the automatic transmission. See, forexample, Japanese Patent Laid-Open No. 2011-208766.

In the structure disclosed in Japanese Patent Laid-Open No. 2011-208766(hereinafter referred to as prior art), an inputting mechanism and shiftposition changing driving means, which is an operation mechanism, aredisposed in such a manner that they are distributed to the left andright sides of a crankcase which serves also as a transmission case. Theinputting mechanism is configured from a shift motor and a speedreduction mechanism for receiving a rotational driving power of theshift motor. Meanwhile, the operation mechanism includes a master armwhich pivots integrally with rotation of the shift spindle and a stoppermember for limiting the amount of the pivotal motion of the master armby being abutted with the master arm. The shift spindle is connected tothe inputting mechanism and the operation mechanism and extendsleftwardly and rightwardly through the inside of the crankcase. Thus,the rotational driving power of the inputting mechanism is transmittedto the operation mechanism through the shift spindle.

In the prior art, when the shifting speed is to be raised, the masterarm is pivoted at a higher pivoting speed. Thereupon, the master arm isabutted with and stopped by the stopper member. However, if the pivotingspeed of the master arm is high, then the impact when the master arm isabutted with the stopper member is high, and this high impact istransmitted to the inputting mechanism through the shift spindle. Inorder to suppress transmission of the impact, in the prior art, theaxial length of the shift spindle is made long so that the shift spindlecan be twisted readily thereby to suppress transmission of the impact tothe inputting mechanism. Further, as the twist angle of the shiftspindle between the inputting mechanism side and the operation mechanismside increases, a greater difference appears between rotational anglesof the shift spindle between the inputting mechanism side and theoperation mechanism side. In order to accurately detect the angle ofrotation of the axial end of the shift spindle on the operationmechanism side, a rotational angle sensor is attached to the axial endof the shift spindle on the operation mechanism side. By adopting such aconfiguration as just described, the prior art can achieve a shiftingoperation of a high accuracy at a high speed by an automatictransmission.

In addition, depending upon the layout of an internal structure of aninternal combustion engine, the inputting mechanism and the operationmechanism for the shift spindle may have to be disposed on the same sideon the outer side of the transmission case.

In this case, the axial length of the shift spindle becomes short andthe shift spindle becomes less likely to be twisted. Therefore, if thepivoting speed of the master arm is high, then when the master arm andthe stopper member are abutted with each other, the impact applied tothe master arm is less likely to be absorbed sufficiently by the shiftspindle. Thus, there is the possibility that the impact may betransmitted to the inputting mechanism through the shift spindle. If theimpact is transmitted to the inputting mechanism, then there is thepossibility that an influence may be hand on the accuracy of theinputting mechanism. In order to raise the strength of the inputtingmechanism to avoid the influence, it is necessary to increase thethickness or the diameter of gears, which gives rise to a problem inupsizing and so forth of the inputting mechanism.

Further, if the rotational angle sensor is attached to the axial end ofthe shift spindle on the operation mechanism side, then the rotationalangle sensor is disposed in the inside of the transmission case.Therefore, it may be difficult to keep the temperature of the rotationalangle sensor lower than an upper temperature limit. Consequently, it issometimes desired to attach the rotational angle sensor to the inputtingmechanism side. However, where the rotational angle sensor is attachedto the inputting mechanism side, if the shift spindle has a twist angle,then the accuracy of the rotational angle sensor may degrade (the valueof the sensor which detects the rotational angle of the shift spindle onthe inputting mechanism side may be displaced from the actual rotationalangle of the shift spindle on the operation mechanism side). Thus, thereis a problem that it is difficult to carry out a shifting operation at ahigh speed and with a high degree of accuracy.

SUMMARY AND OBJECTS OF THE INVENTION

Taking the problem described above into consideration, it is an objectof an embodiment of the present invention to provide a variable speeddrive for an internal combustion engine including a shift motor, wherean inputting mechanism and an operation mechanism are disposed on thesame side on the outer side of a transmission case, wherein a shiftingoperation can be carried out with a high degree of accuracy at a highspeed.

According to an embodiment of the present invention, a variable speeddrive for an internal combustion engine includes a transmission having aplurality of gear trains with a transmission case in which thetransmission is accommodated. An operation mechanism selectivelyestablishes a shift stage of the transmission with a shift spindleconnected to the operation mechanism. An inputting mechanism isconnected to the shift spindle for rotating the shift spindle. Theoperation mechanism includes a master arm pivoted integrally with theshift spindle and a stopper member restricting the amount of the pivotalmovement of the master arm. The shift spindle has an input side endportion to which the inputting mechanism is connected and an output sideend portion supported on a transmission side supporting portion providedon the transmission case. The master arm is positioned between the inputside end portion and the output side end portion in an axial directionof the shift spindle. The master arm includes an extension collar memberfixed integrally thereto with the extension collar member beingconnecting the master arm and a connection portion provided at alocation of the shift spindle rather near to the input side end portionthan the output side end portion. The extension collar member extendsfrom the connection portion toward the master arm with a gap left froman outer circumferential face of the shift spindle.

According to an embodiment of the present invention, a return springbiasing the master arm in a direction to return the master arm to aposition before an operation thereof is provided in the operationmechanism. The return spring has a coiled portion and two end portionsextending from the coiled portion. The shift spindle is formed with adiameter smaller than the inner diameter of the coiled portion of thereturn spring. The shift spindle is disposed so as to extend through thecoiled portion of the return spring with a spring guide collar beinginterposed between the shift spindle and the coiled portion of thereturn spring.

According to an embodiment of the present invention, a washer isinterposed between the extension collar member and the transmission sidesupporting portion.

According to an embodiment of the present invention, spring steel isused for the shift spindle.

According to an embodiment of the present invention, a transmissionincludes a plurality of gear trains with a transmission case in whichthe transmission is accommodated. An operation mechanism selectivelyestablishing a shift stage of the transmission with a shift spindleconnected to the operation mechanism and extending outwardly from thetransmission case. An inputting mechanism is connected to the shiftspindle for rotating the shift spindle. A rotational angle sensordetects the angle of rotation of the shift spindle with the shiftspindle being formed in a hollow cylindrical shape and having an inputside end portion to which the inputting mechanism is connected and anoutput side end portion supported for rotation on a transmission sidesupporting portion of the transmission case. A sensor shaft is insertedin the inside of the shift spindle in a spaced relationship from aninternal circumferential face of the shift spindle with a gap lefttherebetween with the sensor shaft being connected at one end portionthereof to an inner circumferential face of the output side end portionof the shift spindle. The rotational angle sensor is provided at theother end portion of the sensor shaft so as to detect the angle ofrotation of the sensor shaft.

According to an embodiment of the present invention, the master arm isdisposed so as to be positioned between the input side end portion andthe output side end portion of the shift spindle in the axial directionof the shift spindle. Further, the master arm and the output side endportion of the shift spindle are connected to each other by theextension collar member with the gap left from the outer circumferentialface of the shift spindle. Therefore, the substantial axial lengthbetween the inputting mechanism and the master arm is increased withinthe axial length of the shift spindle, and the twist between theinputting mechanism and the master arm can be increased. Further, animpact from the master arm is absorbed by torsional deformation of theextension collar member and the shift spindle. Thus, the impact to betransmitted to the inputting mechanism can be suppressed. Even where theinputting mechanism and the operation mechanism are disposed on the sameside on the outer side of the transmission case, the impact to betransmitted to the inputting mechanism is absorbed. Thus, a shiftingoperation of high accuracy can be carried out at a high speed.

According to an embodiment of the present invention, since the springguide collar is interposed between the shift spindle and the coiledportion of the return spring, the diameter of the shift spindle can bereduced without changing the size of the return spring. Further,displacement of the shift spindle in a diametrical direction can beprevented.

Further, the biasing force of the return spring can be kept fixedwithout the necessity to reduce the return spring in size in conformitywith reduction of the diameter of the shift spindle. Further, as thediameter of the shift spindle decreases, the torsional rigidity of theshift spindle drops. Therefore, it is possible to make the shift spindlelikely to be twisted. Consequently, it is possible to absorb an impactto be transmitted to the inputting mechanism. Thus, a shift operation ofhigh accuracy can be carried out at a high speed.

According to an embodiment of the present invention, since the washer isinterposed between the extension collar member and the transmission sidesupporting portion, abrasion or displacement in rotational movement ofthe extension collar member. Thus, the transmission side supportingportion can be suppressed from being caused by rubbing between them.Especially, when the shift spindle rotates, thrust force in an axialdirection from the return spring acts between the rear end face of theextension collar member and the transmission side supporting portion,and also friction increases. However, since the washer is interposed atthe location, the rotation of the extension collar member or the shiftspindle can be smoothened. Thus, a shift operation of higher accuracycan be carried out.

According to an embodiment of the present invention, spring steel isused for the shift spindle to increase the amount of twist of the shiftspindle. Therefore, an impact to be transmitted to the inputtingmechanism is absorbed. Thus, a shift operation of high accuracy can becarried out at a high speed.

According to an embodiment of the present invention, since the shiftspindle is formed in a hollow cylindrical shape, the torsional rigidityof the shift spindle can be reduced. Further, the sensor shaft isinserted in the inside of the shift spindle in a spaced relationshipfrom the inner circumferential face of the shift spindle with a gap lefttherebetween. Further, the one end portion of the sensor shaft isconnected to the inner circumferential face of the output side endportion of the shift spindle. Furthermore, the rotational angle sensoris provided at the other end portion of the sensor shaft so as to detectthe angle of rotation of the sensor shaft. Therefore, the angle ofrotation of the end portion of the sensor shaft which rotates integrallywith the output side end portion of the shift spindle and has the sameangle of rotation as that of the output side end portion of the shiftspindle can be detected by the rotational angle sensor. Thus, the impactfrom the master arm to be transmitted to the inputting mechanism can besuppressed, and the detection accuracy of the rotational angle sensorcan be made precise. Thus, even in a case in which the inputtingmechanism and the operation mechanism are disposed on the same side onthe outer side of the transmission case, a shift operation of highaccuracy can be carried out at a high speed.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a left side elevational view, partly omitted, of a motorcyclein which a variable speed drive for an internal combustion engineaccording to the present invention is incorporated;

FIG. 2 is a front elevational view of the internal combustion engine asviewed in a direction indicated by an arrow mark II of FIG. 1;

FIG. 3 is a left side elevational view of the internal combustion engineof FIG. 1;

FIG. 4 is a front elevational view depicting a mission holder and achange system holder of the internal combustion engine with a reductiongear holder removed;

FIG. 5 is a sectional view of the transmission taken along line V-V ofFIG. 2;

FIG. 6 is a sectional view of the variable speed drive of the internalcombustion engine taken along line VI-VI of FIG. 3;

FIG. 7 is a partial enlarged view in which a shift spindle and anoperation mechanism are partly enlarged;

FIG. 8 is a partial enlarged view depicting the operation mechanism andthe shift spindle in a partially simplified form; and

FIG. 9 is a front elevational view in a state in which a master arm ispivoted in one direction from the state of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an embodiment of the present invention is describedwith reference to FIGS. 1 to 8.

An internal combustion engine 1, including a variable speed drive 20according to the present embodiment, is a horizontally opposedsix-cylinder water-cooled four-stroke internal combustion engine inwhich a crankshaft 24 extends in a forward and rearward direction of thevehicle, namely, is placed longitudinally on the vehicle, on amotorcycle 2.

The directions forward, rearward, leftward and rightward are definedwith reference to the usual standards wherein the straightforwardlyadvancing direction of the vehicle is the forward direction.

FIG. 1 is a left side elevational view of the motorcycle 2 in which thevariable speed drive 20 of the internal combustion engine 1 according tothe present invention is incorporated. Referring to FIG. 1, intake andexhaust systems, a fuel system and so forth are not depicted.

As depicted in FIG. 1, a vehicle body frame 3 of the motorcycle 2includes a pair of left and right main frames 5, seat rails 6, and backstays 7. The main frames 5 extend rearwardly rather obliquely downwardlyfrom a head pipe 4 at a front portion of the vehicle body and thenextend, at the end portions thereof, downwardly via curved portions 5 a.The seat rails 6 extend rearwardly rather obliquely upwardly from thecurved portions 5 a of the main frames 5. The back stays 7 connect arear portion of the seat rails 6 and a lower portion of the curvedportions 5 a of the main frames 5.

A front fork 8 is supported for leftward and rightward rocking motion onthe head pipe 4 and extends downwardly from the head pipe 4. A frontwheel 9 is supported for rotation at a lower end of the front fork 8,and a steering handlebar 10 is coupled integrally to an upper end of thefront fork 8.

A swing arm 11 is supported at a front end portion thereof for upwardand downward rocking motion by a pivot shaft 12 at a lower portion ofthe curved portions 5 a of the main frames 5 and extends rearwardly. Arear wheel 13 is supported for rotation at a rear end portion of theswing arm 11.

A shock absorber not depicted is connected between the curved portions 5a of the main frames 5 and the swing arm 11, and a riding seat 14 isattached to an upper portion of the seat rail 6.

The internal combustion engine 1 for driving the rear wheel 13 isdisposed below the main frames 5. The internal combustion engine 1 ismounted on the motorcycle 2 by being suspended on a plurality ofattachment brackets 15.

FIG. 2 is a front elevational view of the internal combustion engine 1as viewed in the direction indicated by an arrow mark II in FIG. 1, andFIG. 3 is a left side elevational view of the internal combustion engineof FIG. 1.

As depicted in FIG. 2, the internal combustion engine 1 includes acrankcase 21, cylinder heads 22, and cylinder head covers 23. Thecrankcase 21 is configured from a left crankcase 21 a and a rightcrankcase 21 b. The cylinder heads 22 are coupled to the left and rightends of the crankcase 21. The cylinder head covers 23 are placed on therespective cylinder heads 22.

The crankshaft 24 is supported for rotation between the left crankcase21 a and the right crankcase 21 b and positioned at an upper portion ofthe crankcase 21 such that an axial line thereof is directed in theforward and rearward direction of the motorcycle 2.

Each of pistons (not depicted) in the crankcases 21 a and 21 b isconnected to the crankshaft 24 through a connecting rod (not depicted).Thus, the crankshaft 24 is driven to rotate in an interlockingrelationship with sliding movement of the pistons by combustion incombustion chambers (not depicted).

A front cover 25 is attached to a front face of an upper portion of thecrankcase 21 such that it is centered at the crankshaft 24 and covers anupper portion of a front face of the crankcase 21. Further, a space at alower portion of the crankcase 21 defined by the left crankcase 21 a andthe right crankcase 21 b serves as a transmission chamber 29 in which atransmission 30 hereinafter described is accommodated.

As depicted in FIGS. 2 and 3, a rear cover 18 is attached behind thecrankcase 21, and a clutch cover 19 is attached behind the center of alower portion of the rear cover 18. A mission holder 26 is attached infront of a lower portion of the crankcase 21 such that it covers thefront of the transmission chamber 29. Further, a change system holder 27for holding an operation mechanism 70 for operating the shift stage ofthe transmission 30 is attached to the front face of the mission holder26. The change system holder 27 extends from the center to a lowerportion of the mission holder 26. Furthermore, a reduction gear holder28 for holding an inputting mechanism 50 for supplying power to theoperation mechanism 70 is attached to a left end portion of the frontface of the change system holder 27. A shift motor 51 serving as a powersource for the inputting mechanism 50 is provided at a left end portionof the rear face of the change system holder 27.

A gear transmission mechanism 40, a main shaft 31, a countershaft 32, ashift fork shaft 76 and a shift drum 74 are sub-assembled to a rear faceof the mission holder 26 such that they are configured integrally as acassette unit. If the cassette unit is inserted into the transmissionchamber 29 configured from the left crankcase 21 a and the rightcrankcase 21 b and the mission holder 26 is attached to the front faceof a lower portion of the crankcase 21 in such a manner so as to closeup the front of the transmission chamber 29, then the crankcase 21 andthe mission holder 26 play a role as a transmission case 17. It is to benoted that the cassette unit may be attached to the crankcase 21 in astate in which it is unitized (sub-assembled) together with thereduction gear holder 28 and the shift motor 51.

As depicted in FIGS. 3, 4 and 6, the main shaft 31, countershaft 32,shift fork shaft 76 and shift drum 74 inserted in the transmissionchamber 29 are disposed so as to extend in parallel to the crankshaft24. As depicted in FIG. 2, the main shaft 31 is disposed below thecrankshaft 24, and the countershaft 32 is disposed on the right side ofthe main shaft 31. The shift drum 74 is disposed centrally at a lowerportion of the transmission chamber 29, and two shift fork shafts 76 aredisposed below the main shaft 31 and the countershaft 32 on the left andright sides of the shift drum 74.

FIG. 4 is a sectional view of the transmission 30 taken along line IV-IVof FIG. 2.

As depicted in FIG. 4, the transmission 30 includes the main shaft 31,countershaft 32 and gear transmission mechanism 40 described above, anda clutch mechanism 41. The clutch mechanism 41 is configured as a dualclutch (twin clutch) which has a first hydraulic clutch 41 a and asecond hydraulic clutch 41 b of the hydraulic type.

The main shaft 31 is supported at one end portion thereof for rotationon the mission holder 26 through a ball bearing 33 and has the other endportion disposed so as to extend through a ball bearing 35 attached tothe rear cover 18. The main shaft 31 is supported at a central portionthereof for rotation on the rear cover 18 through the ball bearing 35.

The countershaft 32 is supported at one end portion thereof for rotationon the mission holder 26 through a ball bearing 34 and has the other endportion disposed so as to extend through a ball bearing 36 attached tothe rear cover 18. The countershaft 32 is supported at the other endportion thereof for rotation on the rear cover 18 through the ballbearing 36.

Seven driving transmission gears M from M1 to M7 are provided on themain shaft 31 in a range from one end portion to a central portion ofthe main shaft 31, and corresponding to the driving transmission gearsM, driven transmission gears C from C1 to C7 are provided on thecountershaft 32 such that they normally mesh with the drivingtransmission gears M. Further, reverse sprocket wheels MS and CS areprovided at positions of the main shaft 31 and the countershaft 32 atwhich they mesh with each other, and a chain 39 is provided between thereverse sprocket wheels MS and CS. The gear transmission mechanism 40 isconfigured from the driving transmission gears M, driven transmissiongears C and reverse sprocket wheels S.

The third-speed driving transmission gear M3 is a shifter gear that canslidably move on the main shaft 31 and is selectively placed intoengagement with or disengagement from the fifth-speed drivingtransmission gear M5 or the seventh-speed driving transmission gear M7disposed adjacent the third-speed driving transmission gear M3. Thesixth-speed driving transmission gear M6 is a shifter gear which canslidably move on the main shaft 31 and is selectively placed intoengagement with or disengagement from the fourth-speed drivingtransmission gear M4 or the reverse sprocket wheel MS disposed adjacentthe sixth-speed driving transmission gear M6.

Meanwhile, the fourth-speed driven transmission gear C4 is a shiftergear which can slidably move on the countershaft 32 and is selectivelyplaced into engagement with or disengagement from the second-speeddriven transmission gear C2 or the sixth-speed driven transmission gearC6 disposed adjacent the fourth-speed driven transmission gear C4. Thethird-speed driven transmission gear C3 is a shifter gear that canslidably move on the countershaft 32 and is selectively placed intoengagement with or disengagement from the first-speed driventransmission gear C1 or the fifth-speed driven transmission gear C5disposed adjacent the third-speed driven transmission gear C3.

Each of the shifter gears described above has a fork engaging groove 40a provided thereon and can be slidably moved in an axial directionthereof by a shift fork 77 which engages with the fork engaging groove40 a.

It is to be noted that, for the present gear transmission mechanism 40,a neutral position at which all gear trains are invalid and no power istransmitted and a reverse position provided by the reverse sprocketwheels S are provided.

The clutch mechanism 41 is spline-fitted with the main shaft 31extending through the rear cover 18. The clutch mechanism 41 isconfigured from the first hydraulic clutch 41 a and the second hydraulicclutch 41 b. The other end portion of the main shaft 31 is supported forrotation on the clutch cover 19.

Power of the crankshaft 24 is transmitted to the clutch mechanism 41configured from the first hydraulic clutch 41 a and the second hydraulicclutch 41 b through a primary driving gear 38 a and a primary drivengear 38 b which form a speed reduction mechanism 38. The first hydraulicclutch 41 a or the second hydraulic clutch 41 b is selectively connectedby a hydraulic circuit so that the power is transmitted from thecrankshaft 24 to the main shaft 31.

A secondary driving gear 37 is spline-fitted with the other end portionof the countershaft 32 extending through the rear cover 18. Powertransmitted from the crankshaft 24 to the main shaft 31 is transmittedto the secondary driving gear 37 through a shift stage selectivelyestablished by the gear transmission mechanism 40 and furthertransmitted to the rear wheel 13 (refer to FIG. 1) through a secondarydriven gear 16 a and a drive shaft 16.

FIG. 5 is a front elevational view depicting the mission holder 26 andthe change system holder 27 of the internal combustion engine 1 with thereduction gear holder 28 removed. FIG. 6 is a sectional view of thevariable speed drive of the internal combustion engine 1 taken alongline VI-VI of FIG. 5.

The variable speed drive 20 that carries out shifting by moving theshifter gears of the transmission 30 is described below with referenceto FIGS. 5 and 6.

The variable speed drive 20 includes the inputting mechanism 50 disposedon the outer side of the transmission case 17, a shift spindle 60, andthe operation mechanism 70. Power necessary for shifting is inputtedfrom the shift motor 51 of the inputting mechanism 50 to the shiftspindle 60, and in an interlocking relationship with rotation of theshift spindle 60, the master arm 71 of the operation mechanism 70operates to rotate the shift drum 74 intermittently. Consequently, theshift fork 77 moves the shifter gears of the transmission 30 to carryout changeover of the shift stage.

The inputting mechanism 50 is configured from the shift motor 51 and aspeed reduction gear mechanism 52 connected to the shift motor 51.

As depicted in FIGS. 3 and 6, the shift motor 51 is disposed on a rearface of a left end portion of the change system holder 27 as viewed fromthe front of the vehicle such that an axis of rotation thereof isdirected in the forward and rearward direction so as to extend inparallel to the crankshaft 24.

As depicted in FIG. 6, a motor shaft 51 a is provided on the shift motor51 such that it projects forwardly from the shift motor 51. The motorshaft 51 a is fitted in an opening 27 b formed on a rear face of a leftend portion of the change system holder 27 and is fixed to the changesystem holder 27 from the rear by a bolt 51 c.

An end portion 51 b of the motor shaft 51 a projects from the rear tothe inside of a reduction gear chamber 53 that is formed between thechange system holder 27 and the reduction gear holder 28 and in whichthe speed reduction gear mechanism 52 hereinafter described isaccommodated. A driving gear 52 a for transmitting rotational power ofthe shift motor 51 to the speed reduction gear mechanism 52 isintegrally provided on the end portion 51 b of the motor shaft 51 a.

As depicted in FIGS. 5 and 6, the reduction gear chamber 53 in which thespeed reduction gear mechanism 52 is accommodated is disposed at aposition on the right side in front of the shift motor 51. The speedreduction gear mechanism 52 accommodated in the reduction gear chamber53 is configured from the driving gear 52 a formed integrally on themotor shaft 51 a of the shift motor 51, a first gear 52A, a second gear52B, and a driven gear 52 f in the form of a sector gear. The speedreduction gear mechanism 52 is disposed such that an axis of rotationthereof is directed in parallel to the axis of rotation of the shiftmotor 51.

The first gear 52A and the second gear 52B are supported for rotation onthe change system holder 27 and the reduction gear holder 28, whichconfigure the reduction gear chamber 53, through ball bearings 54 a, 54b, 54 c and 54 d. The driven gear 52 f is fitted against relativerotation on the shift spindle 60 hereinafter described and is supportedsuch that the centers of rotation of the driven gear 52 f and the shiftspindle 60 coincide with each other. The first gear 52A is configuredfrom a first idle gear 52 b of a large diameter and a second idle gear52 c of a small diameter. The second gear 52B is configured from a thirdidle gear 52 d of a large diameter in the form of a sector gear and afourth idle gear 52 e of a small diameter. The driving gear 52 a and thefirst idle gear 52 b, the second idle gear 52 c and the third idle gear52 d, and the fourth idle gear 54 e and the driven gear 52 f normallymesh with each other. Consequently, rotational driving force of theshift motor 51 is transmitted at a reduced speed from the driving gear52 a to the driven gear 52 f.

In this manner, the speed reduction gear mechanism 52 is disposedentirely in the reduction gear chamber 53 formed between the changesystem holder 27 and the reduction gear holder 28. Thus, only if thereduction gear holder 28 is removed as depicted in FIG. 5, the speedreduction gear mechanism 52 is exposed. Consequently, maintenance of thespeed reduction gear mechanism 52 can be readily carried out.

The shift spindle 60 is made of spring steel and is disposed at anobliquely right lower position of the speed reduction gear mechanism 52as viewed in front elevation of the vehicle such that the axialdirection thereof is directed in the forward and rearward direction soas to extend in parallel to the axis of rotation of the shift motor 51.

FIG. 7 is a partial enlarged view in which elements of the variablespeed drive 20 of FIG. 6 around the shift spindle 60 are partlyenlarged.

As depicted in FIGS. 6 and 7, the shift spindle 60 is formed in the formof a hollow cylinder, and an outer circumferential face 60 a of theshift spindle 60 is swollen outwardly to form an increased diameterportion 60 b formed integrally at a location of the shift spindle 60rather forwardly from the center in the axial direction.

As depicted in FIG. 7, from between the opposite end portions of theshift spindle 60, an input side end portion 60 c which is one endportion of the shift spindle 60 on which the driven gear 52 f of thespeed reduction gear mechanism 52 is fitted is supported for rotation onthe reduction gear holder 28 through a ball bearing 61. From between theopposite end portions of the shift spindle 60, an output side endportion 60 d which is the other end portion of the shift spindle 60connected to the operation mechanism 70 hereinafter described issupported for rotation at a transmission side supporting portion 26 aformed on the front face of the mission holder 26, that configures thetransmission case 17, through a needle bearing 62. Further, theincreased diameter portion 60 b of the shift spindle 60 is fitted in anoil seal 63 provided on the change system holder 27 such that it issupported for rotation on the change system holder 27 through the oilseal 63.

In the inside of the shift spindle 60, a sensor shaft 65 separate fromthe shift spindle 60 is disposed such that it is directed in the forwardand rearward direction so as to serve as a center shaft of rotation thesame as that of the shift spindle 60. An inner circumferential face ofthe output side end portion 60 d from within the inner circumferentialface 60 f of the inside of the shift spindle 60 is a small diameterportion 60 g formed with a reduced diameter.

The sensor shaft 65 is formed in a cylindrical shape a little longerthan the shift spindle 60 and is inserted in the inside of the shiftspindle 60 such that it is spaced from the inner circumferential face 60f of the shift spindle 60 with a gap left therebetween. A rear endportion 65 b, that is one end portion of the sensor shaft 65, is forcefitted against relative rotation on the small diameter portion 60 gformed on the inner circumferential face of the output side end portion60 d of the shift spindle 60. The center axes of rotation of the sensorshaft 65 and the shift spindle 60 coincide with each other.

An outer circumferential face 65 c of the sensor shaft 65 contacts onlywith the small diameter portion 60 g from within the innercircumferential face 60 f of the shift spindle 60 while it is spacedfrom the inner circumferential face 60 f at a central portion and theinput side end portion 60 c with a gap left therebetween. The angle ofrotation of a front end portion 65 a which is the other end portion ofthe sensor shaft 65 and the angle of rotation of the output side endportion 60 d of the shift spindle 60 coincide with each other withoutbeing influenced by a twist of the shift spindle 60.

The front end portion 65 a of the sensor shaft 65 projects outwardlyfrom the input side end portion 60 c of the shift spindle 60, andextends through an opening 28 b formed in the reduction gear holder 28,on which the input side end portion 60 c of the shift spindle 60 issupported. Further, the front end portion 65 a of the sensor shaft 65connects to a rotational angle sensor 64 for detecting the angle ofrotation of the shift spindle 60.

As depicted in FIGS. 5 to 7, the rotational angle sensor 64 is disposedon a front face of the reduction gear holder 28 and is positioned infront of the shift spindle 60.

As depicted in FIGS. 6 and 7, the rotational angle sensor 64 is fittedin a sensor attachment recessed portion 28 a formed around the opening28 b of the reduction gear holder 28 and is fixed to the front face ofthe reduction gear holder 28 by a sensor attachment bolt 64 a. Therotational angle sensor 64 detects an angle of rotation of the front endportion 65 a of the sensor shaft 65 to detect the angle of rotation ofthe output side end portion 60 d of the shift spindle 60. In the presentembodiment, a potentiometer of the contact type is used for therotational angle sensor 64. However, it is also possible to use apotentiometer of the non-contact type.

In the present embodiment, the rotational angle sensor 64 is attached tothe front face of the reduction gear holder 28, which is an outer sideof the transmission case 17, in front of the input side end portion 60 cof the shift spindle 60. Therefore, the rotational angle sensor 64 isnot influenced by heat from the combustion chambers or the transmissionchamber 29 which is generated when the rotational angle sensor 64 isattached in the inside of the transmission chamber 29 located behind theoutput side end portion 60 d of the shift spindle 60. Consequently, itis possible to keep the detection accuracy of the rotational anglesensor 64 high, and a shift operation of high accuracy can be carriedout. Further, since the rotational angle sensor 64 is attached to thefront face of the reduction gear holder 28, wiring of the sensor harnessand exchange of the rotational angle sensor 64 can be facilitated.

As depicted in FIGS. 6 and 7, an extension collar member 66 is fittedaround a portion of the shift spindle 60 rather near to the output sideend portion 60 d with a gap left from the outer circumferential face 60a of the shift spindle 60 such that it is directed in the forward andrearward direction and has a center axis of rotation the same as that ofthe shift spindle 60. The extension collar member 66 is provided totransmit rotation of the shift spindle 60 to the master arm 71 of theoperation mechanism 70.

The extension collar member 66 is formed in a cylindrical shape and hasa length same as that of the shift spindle 60 from a connection portion60 e to a portion in the proximity of a central portion in the axialdirection. The extension collar member 66 is serration-fitted at a rearend portion 66 b thereof against relative rotation with the connectionportion 60 e provided at a location of the shift spindle 60 rather nearto the input side end portion 60 c than the output side end portion 60d. Further, the extension collar member 66 is connected at a front endportion 66 a thereof to the master arm 71. In other words, the extensioncollar member 66 extends from the connection portion 60 e of the shiftspindle 60 toward the master arm 71 hereinafter described with a gapleft from the outer circumferential face 60 a of the shift spindle 60.

A washer 67 is interposed between the extension collar member 66 and thetransmission side supporting portion 26 a of the mission holder 26.

The output side end portion 60 d of the shift spindle 60 is fitted inthe washer 67 and prevents abrasion of a rear end face 66 c of theextension collar member 66 and the transmission side supporting portion26 a through rubbing therebetween upon rotation of the shift spindle 60.Further, the washer 67 decreases the frictional resistance of the shiftspindle 60 upon rotation thereby to stabilize rotation of the shiftspindle 60. Meanwhile, when the master arm 71 pivots, a thrust force inan axial direction from a return spring 72 acts between the rear endface 66 c, which is an input side end portion of the extension collarmember 66, and the transmission side supporting portion 26 a. Therefore,there is a tendency that the friction between them increases. However,since the washer 67 is provided at the location, rotation of theextension collar member 66 and the shift spindle 60 is smoothened, and ashift operation of high accuracy can be achieved.

Now, the operation mechanism 70 which interlocks with rotation of theshift spindle 60 to intermittently rotate the shift drum 74 isdescribed.

As depicted in FIG. 6, the operation mechanism 70 includes the masterarm 71, the return spring 72, a stopper member 73, and a pawl ratchetmechanism 78. The master arm 71 is pivoted integrally with rotation ofthe shift spindle 60 through the extension collar member 66. The returnspring 72 biases the master arm 71 so as to return to its positionbefore operation of the master arm 71. The stopper member 73 restrictsthe amount of pivotal motion of the master arm 71. The pawl ratchetmechanism 78 interlocks with pivotal motion of the master arm 71 torotate the shift drum 74 intermittently. The operation mechanism 70 isdisposed in front of the mission holder 26 which configures thetransmission case 17 together with the shift spindle 60 and theinputting mechanism 50, namely, on the outer side of the transmissioncase 17.

FIG. 8 is a partial enlarged view depicting the operation mechanism 70and the shift spindle 60 in a partially simplified form.

As depicted in FIGS. 6 to 8, the master arm 71 is positioned at thecenter between the output side end portion 60 d and the input side endportion 60 c of the shift spindle 60 in the axial direction of the shiftspindle 60. The master arm 71 is disposed so as to connect the shiftspindle 60 and the pawl ratchet mechanism 78 disposed on the right sideof the shift spindle 60 to each other.

As depicted in FIG. 8, the master arm 71 is formed as a plate of asubstantially triangular shape and has a round hole 71 a formed at onecorner portion thereof. The master arm 71 further has a restriction hole71 b of a substantially trapezoidal shape at another corner portionthereof and has a driving hole 71 c of a rounded rectangular shapeprovided at the remaining corner portion thereof.

From among end portions of the restriction hole 71 b, an end portion 71d on the round hole 71 a side is bent to the front face side of themaster arm 71 to form a locking portion 71 e.

As depicted in FIG. 7, the round hole 71 a of the master arm 71 isformed with a diameter equal to the outer diameter of the extensioncollar member 66. The shift spindle 60 and the front end portion 66 a ofthe extension collar member 66 are fitted in the round hole 71 a of themaster arm 71. The extension collar member 66 is welded at the front endportion 66 a thereof integrally to an inner circumferential face 71 f ofthe round hole 71 a of the master arm 71 such that the master arm 71 ispivoted integrally in an interlocking relationship with rotation of theshift spindle 60 around the center axis of rotation of the shift spindle60.

As depicted in FIG. 8, the stopper pin 73 serving as a stopper member isfitted in the restriction hole 71 b of the master arm 71 such that it isdirected in the forward and rearward direction so as to extend inparallel to the axial direction of the shift spindle 60.

The stopper pin 73 is formed in a cylindrical shape smaller than therestriction hole 71 b and force fitted in and fixed to the missionholder 26. When the master arm 71 is pivoted in an interlockingrelationship with rotation of the shift spindle 60, the innercircumference of the restriction hole 71 b is abutted with the stopperpin 73 to restrict the amount of pivotal motion of the master arm 71.

As depicted in FIGS. 6 and 7, the return spring 72 is provided betweenthe extension collar member 66 and the increased diameter portion 60 bof the shift spindle 60 in the axial direction of the shift spindle 60.The return spring 72 biases the master arm 71 in a direction in whichthe master arm 71 returns to the position before operation thereof. Thereturn spring 72 has a coiled portion 72 a, and two end portions 72 bextending from the coiled portion 72 a.

The shift spindle 60 is formed with a diameter smaller than the innerdiameter of the coiled portion 72 a and is disposed on the coiledportion 72 a such that it extends through the coiled portion 72 a.

Further, as depicted in FIG. 8, the two end portions 72 b extend to therestriction hole 71 b along the front face of the master arm 71. The endportions 72 b of the return spring 72 extend to an outer edge of themaster arm 71 in such a manner so as to sandwich the stopper pin 73therebetween together with the locking portion 71 e of the master arm71.

As depicted in FIGS. 7 and 8, a spring guide collar 68 is providedbetween the extension collar member 66 and the increased diameterportion 60 b of the shift spindle 60 in the axial direction of the shiftspindle 60. The spring guide collar 68 is directed in the forward andrearward direction and has the return spring 72 hereinafter describedfitted thereon. The spring guide collar 68 is formed in a cylindricalshape and has an inner diameter substantially equal to the outerdiameter of the shift spindle 60. The spring guide collar 68 isinterposed between the shift spindle 60 and the coiled portion 72 a ofthe return spring 72 for relative rotation to the shift spindle 60.

Since the spring guide collar 68 is interposed between the shift spindle60 and the coiled portion 72 a of the return spring 72, displacement ofthe shift spindle 60 in a diametrical direction is restricted.Therefore, the shift spindle 60 can be formed with a reduced innerdiameter. Further, there is no necessity to reduce the inner diameter ofthe coiled portion 72 a in conformity with the outer diameter of theshift spindle 60, and the diameter of the end portion 72 b is reducedand the biasing force of the return spring 72 does not vary.

FIG. 9 is a front elevational view in a state in which the master arm 71is pivoted in one direction from the state of FIG. 8.

When the shift spindle 60, locking portion 71 e and stopper pin 73 areon the same line in a diametrical direction of the shift spindle 60 asdepicted in FIG. 8, the master arm 71 is in a neutral position. Then, ifthe shift spindle 60 is rotated by an input of driving force from theinputting mechanism 50 and the master arm 71 is pivoted in onedirection, then one of the end portions 72 b of the return spring 72 isheld by the stopper pin 73 while the other end portion 72 b is pushedopen against the spring force of the return spring 72 by the lockingportion 71 e of the master arm 71 as depicted in FIG. 9. Therefore, abiasing force tending to return the master arm 71 to the neutralposition before the operation is applied from the return spring 72 tothe master arm 71.

If the input of driving force from the inputting mechanism 50 stops andthe force having acted upon the master arm 71 through the shift spindle60 disappears, then the master arm 71 is returned to the neutralposition before the operation together with the shift spindle 60 by thereturn spring 72.

As described hereinabove, the amount of pivotal motion of the master arm71 is restricted by abutment of the restriction hole 71 b of the masterarm 71 with the stopper pin 73, and if the shifting speed is raised,then the master arm 71 collides forcefully with the stopper pin 73,whereupon an impact is generated. The impact generated on the master arm71 is transmitted through the extension collar member 66 successively tothe connection portion 60 e of the shift spindle 60, input side endportion 60 c of the shift spindle 60 and driven gear 52 f of the speedreduction gear mechanism 52. Therefore, even if the master arm 71 isdisposed at a position near to the inputting mechanism 50 in the axialdirection of the shift spindle 60, the transmission route of the impactcan be increased by a length equal to the length of the extension collarmember 66 on the same axis without elongating the axial length of theshift spindle 60 itself. Therefore, the impact can be attenuated.Further, the impact to be transmitted from the master arm 71 to theinputting mechanism 50 can be suppressed by torsional deformation of theextension collar member 66 and the shift spindle 60.

As depicted in FIG. 6, the shift drum 74 for shifting the transmission30 is disposed on the rear face of the mission holder 26 in the insideof the transmission chamber 29 such that a shift drum shaft 74 d thereofprojects forwardly from a front end portion 74 a of the shift drum 74.

As depicted in FIGS. 6 and 8, the pawl ratchet mechanism 78 forintermittently rotating the shift drum 74 is provided at a centralportion of the shift drum shaft 74 d in the axial direction.

The pawl ratchet mechanism 78 includes a shift inputting member 79, arotational member 80, and a pair of pawls 81. The shift inputting member79 has formed thereon a driven projection 79 a which is fitted forsliding movement in the driving hole 71 c of the master arm 71. Therotational member 80 rotates integrally with the shift drum 74. Thepawls 81 are built in the rotational member 80 and biased so as toengage with an inner periphery of the rotational member 80. If the shiftinputting member 79 is pivoted in one direction under the guidance ofthe driven projection 79 a which slidably moves in the driving hole 71 cby pivotal motion of the master arm 71, then an end of one of the pawls81 of the pawl ratchet mechanism 78 is erected uprightly and locked bythe rotational member 80. Then, the rotational member 80 is pivoted inan interlocking relationship with the pivotal motion of the shiftinputting member 79 to intermittently rotate the shift drum 74 toestablish a shift stage of the transmission 30.

As depicted in FIG. 6, an engaging groove 74 c is formed on an outercircumferential face 74 b of the shift drum 74, and the shift drum 74 issupported at the front end portion 74 a thereof for rotation on themission holder 26 through a ball bearing 75. If the shift drum 74 isinserted as a cassette unit into the transmission chamber 29, then theshift drum 74 is supported at a rear end portion thereof (not depicted)for rotation on the rear cover 18 through a needle bearing (notdepicted).

The shift fork shafts 76 are disposed on the left and right of the shiftdrum 74 such that they are directed in the forward and rearwarddirection so as to extend in parallel to the shift drum 74. The shiftfork shafts 76 are supported at one end portion thereof on the missionholder 26. If the shift fork shafts 76 are inserted as a cassette unitinto the transmission chamber 29, then they are supported at the otherend portion thereof on the rear cover 18.

Four shift forks 77 (two are not depicted) for moving the shifter gearsof the transmission 30 are supported for sliding movement in the axialdirection on the shift fork shafts 76. Each of the shift forks 77engages at a base portion 77 a thereof with the engaging groove 74 c ofthe shift drum 74 and engages at a tip end portion 77 b thereof with thefork engaging groove 40 a of a shifter gear of the transmission 30(refer to FIG. 4). When the shift drum 74 rotates, the shift fork 77 isslidably moved in the axial direction of the shift fork shaft 76 underthe guidance of the engaging groove 74 c to slidably move the shiftergear of the transmission 30 to selectively establish a shift stage.

As depicted in FIG. 6, a tip end portion 74 e of the shift drum shaft 74d extends through an opening 27 d formed in the change system holder 27and is connected to a shift position sensor 82 for detecting the shiftposition of the shift drum 74.

The shift position sensor 82 is positioned in front of the shift drum 74and disposed on the front face of the change system holder 27. The shiftposition sensor 82 is fitted in a sensor attachment recessed portion 27c formed on the periphery of the opening 27 d of the change systemholder 27 and fixed to the front face of the change system holder 27 bya sensor attachment bolt 82 a. The shift position sensor 82 detects theshift position of the shift drum 74.

An NR detection apparatus 83 for detecting the neutral position and thereverse position of the shift drum 74 and sending a signal to an ECU isprovided on the periphery of the shift position sensor 82 in front ofthe shift drum 74.

The NR detection apparatus 83 includes a position plate 84, a neutralswitch 85, and a reverse position switch 86. The position plate 84rotates integrally with the shift drum shaft 74 d. The neutral switch 85detects that the shift drum 74 and comes to the neutral position byrotation of the position plate 84. The reverse position switch 86detects that the shift drum 74 and comes to the reverse position byrotation of the position plate 84.

The position plate 84 is supported against relative rotation to theshift drum shaft 74 d on the shift drum shaft 74 d between the shiftinputting member 79 and the change system holder 27 in the axialdirection of the shift drum shaft 74 d. The position plate 84 is formedin a shape of a disk, and a flange portion 84 a is integrally formed onan outer circumferential edge of the position plate 84 such that itprojects forwardly. A pin 84 b is force fitted in the inside of theposition plate 84 in a diametrical direction with respect to the flangeportion 84 a.

As depicted in FIG. 6, slidably movable moving elements 85 a and 86 aare provided on the neutral switch 85 and the reverse position switch86, respectively. When the moving elements 85 a and 86 a are pushed inby the pin 84 b or the flange portion 84 a of the position plate 84, theneutral position and the reverse position of the transmission 30 aredetected.

As depicted in FIGS. 5 and 6, the neutral switch 85 is disposed at anoblique left lower position of the front face of the change systemholder 27 with respect to the shift drum shaft 74 d on an orbit of thepin 84 b of the position plate 84. The reverse position switch 86 isdisposed at a position of the front face of the change system holder 27on the left side of the shift drum shaft 74 d on an orbit of the flangeportion 84 a of the position plate 84.

The embodiment of the present invention described above exhibits thefollowing effects.

The master arm 71 is disposed so as to be positioned between the inputside end portion 60 c and the output side end portion 60 d of the shiftspindle 60 in the axial direction of the shift spindle 60. Further, themaster arm 71 and the output side end portion 60 d of the shift spindle60 are connected to each other by the extension collar member 66disposed with a gap left from the outer circumferential face 60 a of theshift spindle 60. In this case, the substantial axial length of theshift spindle 60 between the inputting mechanism 50 and the master arm71 can be increased by a length equal to the length of the extensioncollar member 66 within the axial length of the shift spindle 60. Thetwist between the inputting mechanism 50 and the master arm 71 can beincreased by a length equal to the length of the extension collar member66. Thus, even in a case in which the inputting mechanism 50 and theoperation mechanism 70 are disposed on the same side on the outer sideof the transmission case 17, an impact from the master arm 71transmitted to the inputting mechanism 50 can be absorbed by torsionaldeformation of the extension collar member 66 and the shift spindle 60and can be suppressed. Thus, a shift operation of high accuracy can becarried out at a high speed.

The impact from the master arm 71 is transmitted through the extensioncollar member 66 successively to the connection portion 60 e of theshift spindle 60, the input side end portion 60 c of the shift spindle60 and the driven gear 52 f of the speed reduction gear mechanism 52.Thus, the transmission route of the impact can be elongated on the sameaxis without increasing the axial length of the shift spindle 60.Consequently, also in a layout in which the length of the shift spindle60 is short, it is possible to attenuate the impact from the master arm71 to be transmitted to the inputting mechanism 50. Thus, a shiftoperation of high accuracy can be carried out at a high speed.

Since the spring guide collar 68 is interposed between the shift spindle60 and the coiled portion 72 a of the return spring 72, the diameter ofthe shift spindle 60 can be reduced without changing the size of thereturn spring 72 and displacement of the shift spindle 60 in adiametrical direction can be prevented. Consequently, a shift operationof higher accuracy can be carried out.

The biasing force of the return spring 72 can be kept fixed without thenecessity to decrease the size of the return spring 72 in conformitywith a reduction of the diameter of the shift spindle 60. Further, asthe diameter of the shift spindle 60 decreases, the torsional rigidityof the shift spindle 60 drops, and therefore, the shift spindle 60 canbe made likely to be twisted. Thus, it is possible to absorb an impactto be transmitted to the inputting mechanism 50, and consequently, ashift operation of high accuracy can be carried out at a high speed.

Since the washer 67 is interposed between the rear end face 66 c of theextension collar member 66 and the transmission side supporting portion26 a, abrasion or displacement in rotational movement of the rear endface 66 c of the extension collar member 66 and the transmission sidesupporting portion 26 a can be prevented from being caused by rubbingbetween them. Especially, when the shift spindle 60 rotates, a thrustforce in an axial direction from the return spring 72 acts between therear end face 66 c of the extension collar member 66 and thetransmission side supporting portion 26 a, and also friction increases.However, since the washer 67 is interposed at the location, the rotationof the extension collar member 66 or the shift spindle 60 can besmoothened, and consequently, a shift operation of higher accuracy canbe carried out.

Spring steel is used for the shift spindle 60 to improve the modulus ofelasticity of the shift spindle 60 itself. Therefore, the shift spindle60 is likely to be twisted, and an impact to be transmitted to theinputting mechanism 50 is absorbed. Consequently, a shift operation ofhigh accuracy can be carried out at a high speed.

Since the shift spindle 60 is formed in a hollow cylindrical shape, thetorsional rigidity of the shift spindle 60 drops, and the shift spindle60 can be made likely to be twisted. Consequently, an impact to betransmitted to the inputting mechanism 50 can be absorbed, and a shiftoperation of high accuracy can be carried out at a high speed.

The sensor shaft 65 is inserted in the inside of the shift spindle 60 ina spaced relationship from the inner circumferential face 60 f of theshift spindle 60 with a gap left therebetween. Further, the rear endportion 65 b which is one end portion of the sensor shaft 65 isconnected to the inner circumferential face 60 f of the output side endportion 60 d of the shift spindle 60. Further, the rotational anglesensor 64 is connected to the front end portion 65 a, which is the otherend portion of the sensor shaft 65, so as to detect the angle ofrotation of the sensor shaft 65. Therefore, the angle of rotation of theoutput side end portion 60 d of the shift spindle 60 fixed integrally tothe sensor shaft 65 can be detected by the rotational angle sensor 64.Consequently, the detection accuracy of the rotational angle sensor 64can be made precise. Thus, a shift operation of high accuracy can becarried out.

Since the rotational angle sensor 64 is attached to the front face ofthe reduction gear holder 28 on the outer side of the transmission case17, it is not influenced by heat from the combustion chambers or thetransmission chamber 29 generated where the rotational angle sensor 64is attached in the transmission chamber 29 behind the output side endportion 60 d of the shift spindle 60. Consequently, the detectionaccuracy of the rotational angle sensor 64 can be kept high, and a shiftoperation of high accuracy can be carried out. Further, since therotational angle sensor 64 is attached to the front face of thereduction gear holder 28, wiring of a harness for the sensor andexchange of the rotational angle sensor 64 can be facilitated.

Where the inputting mechanism 50, shift spindle 60 and operationmechanism 70 are disposed on the same side in front of the missionholder 26 which configures the transmission case 17 as in the presentembodiment, in other words, even if the components mentioned aredisposed on the outer side of the transmission case 17, the rotationalangle sensor 64 can be attached to the front face of the reduction gearholder 28 on the outer side of the transmission case 17. Therefore, therotational angle sensor 64 is not influenced by heat generated where itis attached in the transmission chamber 29 behind the output side endportion 60 d of the shift spindle 60. Consequently, the detectionaccuracy of the rotational angle sensor 64 can be kept high, and a shiftoperation of high accuracy can be carried out.

While the present embodiment has been described with reference to thedrawings, the embodiment is not limited to the substance of theforegoing description and can be modified without departing from thesubject matter of the present invention.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A variable speed drive for an internal combustionengine, comprising: a transmission having a plurality of gear trains; atransmission case for accommodating the transmission; an operationmechanism selectively establishing a shift stage of the transmission; ashift spindle operatively connected to the operation mechanism; and aninputting mechanism operatively connected to the shift spindle forrotating the shift spindle; the operation mechanism including a masterarm pivoted integrally with the shift spindle and a stopper memberrestricting the amount of the pivotal movement of the master arm; theshift spindle having an input side end portion to which the inputtingmechanism is connected and an output side end portion supported forrotation on a transmission side supporting portion provided on thetransmission case; the master arm being positioned between the inputside end portion and the output side end portion in an axial directionof the shift spindle; the master arm having an extension collar memberfixed integrally thereto; the extension collar member connecting themaster arm and a connection portion provided at a location of the shiftspindle rather near to the input side end portion than the output sideend portion; the extension collar member extending from the connectionportion toward the master arm with a gap left from an outercircumferential face of the shift spindle.
 2. The variable speed drivefor an internal combustion engine according to claim 1, wherein a returnspring biasing the master arm in a direction to return the master arm toa position before an operation thereof is provided in the operationmechanism; the return spring includes a coiled portion and two endportions extending from the coiled portion; the shift spindle is formedwith a diameter smaller than the inner diameter of the coiled portion ofthe return spring; the shift spindle is disposed so as to extend throughthe coiled portion of the return spring; and a spring guide collar isinterposed between the shift spindle and the coiled portion of thereturn spring.
 3. The variable speed drive for an internal combustionengine according to claim 2, wherein a washer is interposed between theextension collar member and the transmission side supporting portion. 4.The variable speed drive for an internal combustion engine according toclaim 1, wherein spring steel is used for the shift spindle.
 5. Avariable speed drive for an internal combustion engine, comprising: atransmission having a plurality of gear trains; a transmission case foraccommodating the transmission; an operation mechanism for selectivelyestablishing a shift stage of the transmission; a shift spindleoperatively connected to the operation mechanism and extending outwardlyfrom the transmission case; an inputting mechanism operatively connectedto the shift spindle for rotating the shift spindle; and a rotationalangle sensor detecting the angle of rotation of the shift spindle; theshift spindle being formed in a hollow cylindrical shape and having aninput side end portion to which the inputting mechanism is connected andan output side end portion supported for rotation on a transmission sidesupporting portion of the transmission case; a sensor shaft beinginserted in the inside of the shift spindle in a spaced relationshipfrom an internal circumferential face of the shift spindle with a gapleft therebetween; the sensor shaft being connected at one end portionthereof to an inner circumferential face of the output side end portionof the shift spindle; the rotational angle sensor being provided at theother end portion of the sensor shaft so as to detect the angle ofrotation of the sensor shaft.
 6. The variable speed drive for aninternal combustion engine according to claim 5, wherein the operationmechanism includes a master arm pivoted integrally with the shiftspindle and a stopper member restricting the amount of the pivotalmovement of the master arm; the shift spindle having an input side endportion to which the inputting mechanism is connected and an output sideend portion supported for rotation on a transmission side supportingportion provided on the transmission case; the master arm beingpositioned between the input side end portion and the output side endportion in an axial direction of the shift spindle; the master armhaving an extension collar member fixed integrally thereto; theextension collar member connecting the master arm and a connectionportion provided at a location of the shift spindle rather near to theinput side end portion than the output side end portion; the extensioncollar member extending from the connection portion toward the masterarm with a gap left from an outer circumferential face of the shiftspindle.
 7. The variable speed drive for an internal combustion engineaccording to claim 6, wherein the operation mechanism includes a returnspring biasing the master arm in a direction to return the master arm toa position before an operation thereof; the return spring includes acoiled portion and two end portions extending from the coiled portion;the shift spindle is formed with a diameter smaller than the innerdiameter of the coiled portion of the return spring; the shift spindleis disposed so as to extend through the coiled portion of the returnspring; and a spring guide collar is interposed between the shiftspindle and the coiled portion of the return spring.
 8. The variablespeed drive for an internal combustion engine according to claim 7,wherein a washer is interposed between the extension collar member andthe transmission side supporting portion.
 9. The variable speed drivefor an internal combustion engine according to claim 6, wherein springsteel is used for the shift spindle.
 10. A variable speed drive for aninternal combustion engine, comprising: a transmission having aplurality of gear trains; an operation mechanism selectivelyestablishing a shift stage of the transmission; a shift spindleoperatively connected to the operation mechanism; and an inputtingmechanism operatively connected to the shift spindle for rotating theshift spindle; the operation mechanism including a master arm pivotedintegrally with the shift spindle and a stopper member restricting theamount of the pivotal movement of the master arm; the shift spindlehaving an input side end portion to which the inputting mechanism isconnected and an output side end portion supported for rotation on atransmission side supporting portion; the master arm being positionedbetween the input side end portion and the output side end portion in anaxial direction of the shift spindle; the master arm having an extensioncollar member fixed integrally thereto; the extension collar memberconnecting the master arm and a connection portion provided at alocation of the shift spindle rather near to the input side end portionthan the output side end portion; the extension collar member extendingfrom the connection portion toward the master arm with a gap left froman outer circumferential face of the shift spindle.
 11. The variablespeed drive for an internal combustion engine according to claim 10,wherein a return spring biasing the master arm in a direction to returnthe master arm to a position before an operation thereof is provided inthe operation mechanism; the return spring includes a coiled portion andtwo end portions extending from the coiled portion; the shift spindle isformed with a diameter smaller than the inner diameter of the coiledportion of the return spring; the shift spindle is disposed so as toextend through the coiled portion of the return spring; and a springguide collar is interposed between the shift spindle and the coiledportion of the return spring.
 12. The variable speed drive for aninternal combustion engine according to claim 11, wherein a washer isinterposed between the extension collar member and the transmission sidesupporting portion.
 13. The variable speed drive for an internalcombustion engine according to claim 10, wherein spring steel is usedfor the shift spindle.